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Summary

A 3-D regional electrical conductivity model of the crust and upper mantle beneath the Yellowstone/Snake River Plain volcanic province (Idaho and Wyoming, United States) based on magnetotelluric data, Kelbert, Egbert, and deGroot-Hedlin (2012) .

The lowest resistivities in the area can only plausibly be explained by partial melt and/or fluids, providing valuable new information about the distribution of these phases deep within the Earth beneath the volcanic system. Unexpectedly, in light of the mantle plume models often used to explain Yellowstone volcanism, the electromagnetic data imply that there is no interconnected melt in the lower crust and uppermost mantle directly beneath the modern Yellowstone caldera. Instead, low resistivities consistent with 1-3% melt in the uppermost mantle (depths of 40-80 km) extend at least 200 km southwest of Yellowstone. Shallower areas of reduced resistivity extend upward into the mid-crust around the edges of the seemingly impermeable Snake River Plain province, including beneath Yellowstone.

We suggest that the elevated temperatures beneath the active volcanic center have resulted in greater permeability, allowing magma to ascend to shallower depths and pool in the crust. Little melt is entering the system from below at present, perhaps due to intermittency of supply.

Authors:

A. Kelbert

College of Earth, Ocean and Atmospheric Sciences

Oregon State University

Corvallis, Oregon 97331, USA

G. D. Egbert

College of Earth, Ocean and Atmospheric Sciences

Oregon State University

Corvallis, Oregon 97331, USA

C. deGroot-Hedlin

Scripps Institution of Oceanography

University of California

San Diego, La Jolla, California 92037, USA

Previous Model

N/A

Reference Model

N/A

Prior Model

200 Ohm*m halfspace

Inversion Software

Modular System for Electromagnetic Inversion, Egbert and Kelbert (2012)

Frequency domain long-period (10 to 1e4 secs) magnetotelluric (MT) data from 91 EarthScope MT sites, covering much of Idaho and Wyoming, southern Montana, eastern Oregon and northern Nevada, together with 32 sites from an earlier MT survey collected by C. deGroot-Hedlin in two denser profiles along and across the eastern SRP.

Figure shows 3-D views of the magmatic system beneath the Snake River Plain/Yellowstone volcanic province, as inferred from magnetotelluric data. The isosurface of 40 Ohm*m and below resistivities; data locations are plotted on top. Yellowstone is indicated with an open circle. Note the conductive pathway to the Yellowstone caldera from beneath the eastern Snake River Plain.

Figure shows 3-D views of the magmatic system beneath the Snake River Plain/Yellowstone volcanic province, as inferred from magnetotelluric data. Three cross-sections that show log10 conductivities (S/m) in the same area.